1. Field of the Invention
The present invention is directed to a drill bit and, more particularly, to a drill bit which includes passages for carrying drilling fluid to the exterior sides of the drill bit for forming a fluid layer between exterior side portions of the drill bit and the side wall of a bore hole.
2. Description of the Prior Art
In prior art downhole devices such as drill bits, there is generally some contact between the sides of the downhole device and the sides of the borehole. The contact between the device and the side of the borehole causes friction which results in the wearing of that portion of the downhole device which contacts the side of the bore hole.
One example of a typical prior art downhole device which has contact between the side of the device and the side of the borehole is a drill bit with a single conical cutter head such as that shown in U.S. Pat. No. 4,154,312 and by co-pending application Ser. No. 153,683, filed May 27, 1980, both of which are incorporated herein by reference. In the single conical cutter head of the type shown, the drilling action of the bit produces a force which pushes side portions of the bit against the side wall of the borehole, which produces a lateral reaction force. The lateral force tends to drive the bit body to turn eccentrically in the direction diametrically opposite to the line of radial contact of the conical head with the well bottom. The lateral force causes friction and results in wear on that portion of the bit body.
Furthermore, in drill bits of this type, in order to make the drill bit turn on its true geometric axis, it has been necessary to use a stabilizer or centralizer. The stabilizer is generally made of a very hard material in order to reduce wear and prolong its life. The need for the stabilizers and the necessity for making the stabilizer of a hard material significantly increases the cost of the drill bit and, although increasing the life of the drill bit as compared to one without a stabilizer or without some type of hard material to reduce wear, these types of prior art devices are still subject to wear and, therefore, required fairly frequent replacement.
In considering the use of drill bits such as those described, namely, for drilling in the earth's crust for oil, water or minerals, the environment is very hostile to the drill bit. Thus, the drill bit is subject to extreme wear. Furthermore, especially when drilling for oil, the depth of the drill string is extremely long as, for example, in the area of 5,000 to 10,000 feet. Thus, the raising of the drill string to replace the drill bit requires a great deal of time and is, therefore, very expensive because during this time period, no drilling can take place.